Cyclophosphamide is an anticancer drug used in the treatment of a variety of cancers. It is administered in inactive form and is activated in the liver cytochrome P-450 pathway. After activation, the cytotoxic metabolites include phosphoramide mustard. Phosphoramide mustard forms DNA cross-links between (interstrand crosslinkages) and within (intra-strand crosslinkages) DNA strands at guanine N-7 positions. This leads to cell death. While the cytotoxic metabolites produce the desired anticancer effect in tumor tissues, it is also distributed to normal tissues where it causes adverse effects.
Peptide conjugates are formed by attaching a chemotherapeutic agent to a peptide either directly or through a linker. They are designed so the chemotherapeutic agent is inactive until the conjugate is cleaved by a tumor-specific enzyme in close proximity to tumor tissues. This increases the selectivity of the chemotherapeutic agent in killing cancer cells while decreasing adverse effects elsewhere in the system.
The peptides may be attached to the chemotherapeutic drugs either directly or through a linker. U.S. Pat. No. 7,091,186, for example, discloses self-immolative linkers that allow the release of fully active, chemically unmodified drug from the peptide. However, the methods of using such linkers disclosed in the '186 patent are not suitable for use with phosphoramide chemotherapeutic drugs. Accordingly, there is still a need in the art for methods of synthesis of phosphoramide chemotherapeutic conjugates.